As shown in FIGS. 1 and 2, a conventional bicycle front fork 10 is provided with an inverted U-shaped locating frame 13 which is fastened with two upright tubes 11 and 12 of the front fork 10. Two guide supports 14 and 15 are fastened pivotally with the locating frame 13 such that the first guide support 14 is used to support a first brake shoe 16, and that the second guide support 15 is used to support a second brake shoe 17. The brake shoes 16 and 17 are respectively actuated by the guide supports 14 and 15, which are linked with a brake cable 1. The brake cable I is put through the top of the first guide support 14 such that one end of the brake cable 1 is fastened with the top of the second guide support 15 by a fastening screw 18. When the brake cable 1 is pulled to slow down or stop the bicycle in motion, the brake shoes 16 and 17 are not evenly exerted on by the pull force of the brake cable 1 because the two guide supports 14 and 15 are different in amplitude when they swivel. As a result, the braking effect of the two brake shoes 16 and 17 is seriously undermined. In addition, the two brake shoes 16 and 17 are different in the extent to which they are worn.